Existing trenchless methods for the structural renovation of drinking water pipelines rely on the insertion of a moulded material, such as a polyethylene pipe or liner, inside an existing pipe. The three main trenchless technologies employed for this purpose can be summarised according to the following:
Pipe in Pipe Method
A moulded (e.g. polyethylene) pipe with a diameter smaller than that of the existing pipe is either pulled or pushed into the existing pipe. By virtue of being an extremely simple method, it has been used to renovate not only drinking water pipelines, but many other pipeline infrastructures. However, the method does have its shortcomings. For example, as insertion resistance increases over long spans, the length and complexity of pipes is limited. Furthermore, it is also necessary to consider the reduction in supply capacity of a pipe renovated by this method as a result of the annular gap between the existing pipe and the internal pipe.
Pipe Bursting Method
The method, as the name implies, is executed by expansion and cracking of the existing pipe by insertion of a hydraulic expander inside it, accompanied by insertion of a moulded polyethylene pipe into the space thus formed. Benefits of this method are the simplicity of use and the ability to install pipes with an equivalent or larger diameter than the existing pipe. However, disadvantages are the potential damage to other infrastructures in urban environments, and the difficulty in disposing of residual pipe fragments.
Polyethylene Thin Wall Lining (PETWL)
A folded polyethylene liner is inserted into the existing pipe and pressure applied to produce a “close fit” liner, which is subsequently held in place by the water pressure within the pipeline.
All three of the above methods are disadvantaged by their inability to deal with multiple bends in a pipeline and, more importantly, the fact that lateral connection pipes to customers' premises have to be disconnected and then reinstated after execution of the renovation process.
A need therefore exists for a renovation method which has the capability to accommodate long pipe spans (up to 200 meters) and pipe bends, and which obviates the necessity for reinstatement of lateral connection pipes.